1. Field of the Invention
The present invention relates to the fermentation microbiological industry, and specifically to a method for producing an L-amino acid using a bacterium of the Enterobacteriaceae family, wherein the bacterium has been modified so as to not produce type I fimbrial adhesin protein. L-amino acids are employed as components of pharmaceuticals, animal feed additives, seasonings, and various other nutritive mixtures.
2. Brief Description of the Related Art
L-amino acids are industrially produced by fermentation using L-amino-acid producing bacteria such as coryneform bacteria and the genus Escherichia. To enhance productivity, artificially mutated strains of these bacteria that have been isolated from nature or transformants in which activity of an L-amino acid biosynthesis enzyme has been increased by genetic recombination have been employed as the L-amino acid producing bacteria. (U.S. Pat. Nos. 5,661,012, 6,040,160, 5,827,698, 5,932,453, and WO01/53459)
In addition to methods of increasing the level of expression of enzymes which are a part of L-amino acid biosynthesis pathways, other methods of increasing the ability to produce L-amino acids such as L-lysine have been developed. Such methods include improving energy efficiency by modifying the energy pathway (EP1170376), increasing the ability to produce nicotinamide adenine dinucleotide phosphoric acid by amplifying the nicotinamide nucleotide transhydrogenase gene (U.S. Pat. No. 5,830,716), and inactivating genes related to flagella production (WO02/097089).
Escherichia, Salmonella, and Bacillus bacteria have fimbriae. Fimbriae can be divided into types I to V which have no direct relation to sexual processes such as conjugation and gene transfer, and sexual fimbriae that are produced on the outer layers of donor bacteria and are essential to conjugation with recipient bacteria and to gene transfer (Shoji Mizushima, Kinichiro Miura, Bacterial Anatomy 129 (1979)).
There are nine genes which contribute to the formation of type I fimbriae, and these genes form an operon. The fimH gene, located downstream within the operon, encodes a type I fimbrial adhesin protein. Type I fimbrial adhesin protein does not contribute to the formation of fimbriae, but is known to specifically recognize the mannosylated proteins of the host. Furthermore, it is known that the capacity for bacterial aggregation can be enhanced by introducing an amino acid substitution into the gene which encodes the type I fimbrial adhesin protein (Mark A. Schenbri, Gunna Christiansen and Per Klemm: FimH-mediated auto aggregation of Escherichia coli: Molecular Microbiology (2001) 41 (6), 1419-1430). However, there is no information relating to the relationship between the effect of introducing a mutation which causes reduction in the adhesion activity of type I fimbrial adhesin protein and L-amino acid production.